The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Uninterruptible power supplies (UPSs) are used in supplying power to data centers. In this regard, UPSs in addition to providing back-up power to the data centers in the event of interruption of power from an electric utility, may also condition the power from the electric utility. An electric utility substation down converts utility power to generate substation power that is supplied to the UPSs, which conditions the substation power. Each of the UPSs has a source of backup power that provides power in the event of an interruption in the utility power. The UPSs may supply power to, for example, one or more power supplies of one or more servers of the data center.
A data center may have multiple loads (e.g., servers). Each of the loads has a power supply (load power supply) that may operate over a range of input voltages. Efficiency of the load power supplies may vary based on their input voltages. As such, each load power supply may have a corresponding input voltage at which the load power supply operates at a maximum efficiency level. For example, a load power supply may be capable of operating with input voltages ranging from 208 VAC to 240 VAC. The load power supply may however operate at a maximum efficiency level when it has a 240 VAC input voltage. In this regard, commonly used server power supplies in the United States typically operate at a maximum efficiency when their input voltages are 240 VAC.
One or more uninterruptible power supplies (UPSs) may be used to provide output voltage(s) to the load power supplies of the data center. The UPSs receive power from a substation at a substation voltage (e.g., 208 VAC) and may each be configured to provide output power at a fixed nominal output voltage. The UPS may typically have a UPS mode and a bypass mode. When in the UPS mode, the UPSs may regulate, filter and condition a substation voltage to provide the output power. Each of the UPSs may include a bypass switch that, when the UPS is in the bypass mode, is in a bypass state (e.g., closed) and provides the power from the utility at the substation voltage directly to the load power supplies. This may be performed when a failure occurs in the UPS or the input power from the utility is clean enough that conditioning is not required. In the bypass mode, components (e.g., transformers, rectifier(s), inverter(s), etc.) of a UPS are bypassed to provide the power from the utility at the substation voltage directly to the output of the UPS and thus directly to the load power supplies.
If the UPSs are configured to raise the voltage of the power from the substation voltage (referred to herein as the “static bypass voltage”) to higher voltages than the substation voltage, such as 240 VAC, for maximum operating efficiencies of the load power supplies (referred to herein as “efficient voltages”), the output voltages of the UPSs may suddenly drop. This may occur when the UPS switches from the UPS mode to the bypass mode. Using the United States as an example, when a UPS switches from the UPS mode to the bypass mode, the output voltage of the UPS may suddenly drop from an efficient voltage level of 240 VAC to the static bypass voltage level of 208 VAC. This sudden drop in voltage can negatively affect operation of the load power supplies and/or the corresponding loads.
To prevent voltage drops during bypass events, the UPSs may be configured to provide the same output voltage(s) in UPS mode to the load power supplies that are provided during bypass mode, such as a 208 VAC output in each mode. This however prevents the load power supplies and/or the corresponding loads from operating at maximum efficiency levels.